Single-ply Membranes

Single-ply membranes are factory-manufactured sheet membranes. They generally are categorized as either thermoplastic or thermoset. Thermoplastic materials can be repeatedly softened when heated and hardened when cooled. Thermoset materials solidify, or “set,” irreversibly after heating. Single ply membranes commonly are referred to by their chemical acronyms, such as ethylene propylene diene terpolymer (EPDM).

Single-ply sheet membranes are produced using one of three manufacturing processes: calendering, extruding or spread coating. The membranes may contain reinforcement layers. Common reinforcements for single ply membranes include polyester fabrics or scrims, glass fiber, or a felt or fleece backing.

A finished sheet’s thickness typically is referred to as mil thickness; 1 mil equals 0.001 inch. Common mil thicknesses for these sheet membranes range from 30 mils to 60 mils.

Single-ply membranes can be installed fully adhered, mechanically attached or held down with ballast. Most single-ply roof systems do not receive surfacing.

In many instances, a combination of attachment methods are used to secure a roof system. For instance, an insulation may be mechanically attached to the substrate with the roof membrane fully adhered to the insulation.

The most common thermoplastic roof membranes are PVC and TPO. The following provides general descriptions of these two systems.

Polyvinyl Chloride (PVC)

PVC sheets are produced by calendaring, spread coating or extruding, and typically are reinforced with polyester or glass-fiber mats or scrim. PVC sheets contain plasticizers and stabilizers, as well as other additives to impart flexibility and achieve other desired physical properties. Some membranes are available with nonwoven fleece backing adhered to the underside of a sheet.

• Sheet widths range from 6 feet to 12 feet wide.

• Sheets are typically 45mil to 135mil mils thick.

• Seams are sealed by heat or chemical welding.

• PVC membranes are produced in numerous colors, though gray and white are the most common.

Thermoplastic Olefin (TPO)

TPO membranes are produced by calendering with lamination, extrusion with lamination, or extrusion-coating techniques. TPO sheets are a blend of polypropylene and ethylene propylene polymers and usually are reinforced with polyester. TPO sheets contain colorant, flame retardants, UV absorbers and other proprietary substances to achieve desired physical properties.

• Sheet widths range from 6 feet to 12 feet wide

• Sheets are typically 45mil to 135mil mils thick

• Seams are sealed by heat welded with hot air

• TPO membranes commonly are white

Ethylene Propylene Diene Terpolymer (EPDM)

EPDM principally is composed of two compounds, ethylene and propylene, that are derived from oil and natural gas. The following are some characteristics of EPDM roof membranes: